超临界CO2 对煤体微观孔隙结构非均质性及连通性的影响OA

Supercritical CO2 fracturing technology can not only improve coalbed methane recovery but also realize in-situ CO2 se-questration.Supercritical CO2 soaking modification experiments were carried out on coal samples collected from Huanghou Coal Mine in Yangquan.Combined with low-temperature N2 and low-pressure CO2 adsorption tests,the differences in the microporous and mesoporous structure of coal samples before and after modification were characterized.Based on the multifractal theory,the changes in pore size distribution heterogeneity and connectivity were quantitatively analyzed.The results show that supercritical CO2 treatment promotes pore development of coal samples:the number of mesopores increases significantly,while the number of micro-pores decreases relatively.After treatment,the N2 adsorption capacity of coal samples increases,the adsorption-desorption hysteresis weakens,the pore inlet and outlet become wider,the retention effect decreases,and the pore connectivity is enhanced.The hetero-geneity of micropore size distribution decreases with significantly improved connectivity,whereas the heterogeneity of mesopore size distribution increases with reduced connectivity.Compared with raw coal,coal samples treated by supercritical CO2 show over-all enhanced pore connectivity,which is conducive to improving coal reservoir permeability.The pore surface becomes rougher,the pore size distribution is more uneven,and the complexity of the pore structure is significantly improved.The metamorphic degree and maceral composition of coal jointly affect the heterogeneity and connectivity of the pore structure.High-rank coal has a complex pore microstructure,and its connectivity is significantly improved after CO2 treatment.For low-rank coal,the permeability enhance-ment effect lags under the action of CO2 extraction and swelling.Supercritical CO2 modification endows the coal with higher pore heterogeneity over a wider pore size range and forms a more connected pore-fracture network.